The central premise for ACTG 392 is that many HIV-infected individuals with prior weight loss, the failure to regain weight and lean tissue is at least in part the consequence of inadequate quantity or the quality of protein ingested rather than total energy intake, which may even be substantially above anticipated caloric needs. Dietary sources of protein are presumably inadequate to compensate for the increased release of amino acids from muscle and enterocytes to meet high metabolic needs caused by HIV infection (e.g., increased turnover of lymphocytes). As with most catabolic conditions, it is probable that HIV patients ingesting excess calories with insufficient protein substrates generate additional increases in REE to metabolize these excess calories-presumably due to increased lipogenesis and catecholamine release which may contribute to the inability to gain lean tissue. Moreover, the excess non-protein energy may be converted to visceral fat. Finally, there may also be periods in which the lack of sufficient protein intake may be complicated by inadequate intake of non-protein calories resulting in further weight loss. This is a phase II, 12-week, double-blind, proof of concept study involving subjects with stable weight loss and no evidence of active opportunistic complications or malabsorption. Two groups of 28 subjects (about 5 subjects at this study site) each will be randomly chosen to receive either an oral nutritional supplement containing increased amounts of high quality protein (whey), which is rich in cystine and glutamine from a conventional source or an isocaloric, identical tasting supplement without added whey protein. The supplements will be administered mid-morning and mid-afternoon between meals. Weight, body composition, anthropometry, dietary intake, and overall health status assessment will be assessed at Baseline and Weeks 6 and 12. Plasma cystine, glutathione, C-reactive protein, and pre-albumin, along with urine IL-6, sTNFrII, and IL-1ra, will be assessed at baseline and Week 12.